Dehydrating process



Jan. 22, 1935. G, D. ARNOLD DEHYDRATING PROCESS Original Filed March 1,1930 3 Sheets-Sheet l Jan. 22, 1935. G. D. ARNOLD DEHYDRATING PROCESSOriginal Filed March 1, 1930 3 Sheets-Sheet 2 a as yaw gwuentoc MNSILD.M

Jan. 22, 1935. G. D. ARNOLD DEHYDRATING PROCESS Original Filed March 1,1930 3 Sheets-Sheet 3 gwoemtoz Patented Jan. 22, 1935 UNITED STATESPATENT OFFICE Divided and this application March 25, 1931, Serial No.525,218

8 Claims.

This invention relates to improvements in dehydrating processes. Thisapplication is a division of my application Serial No. 432,366, filedMarch 1, 1930.

Broadly stated, it is the primary object of the present invention toprovide a drying process which will economically handle large quantitiesof material and rapidly dehydrate such material with a minimumexpenditure of energy and an accurate control of the extent ofdehydration.

More specifically stated, I propose to use relatively large volumes ofheated air and gas in the dehydrating operation, to convey pneumaticallythe material to be dehydrated through a chamber of increasing crosssection through which the material can only move when it is dehydratedsufficiently to respond to the decreased velocity of fluid currents; toconduct the entire dehydrating operation at pressures less thanatmospheric; and to operate under such complete control as to deliver asubstantially uniformly dried product. It is most important to theachievement of this last objective, that all air should be excluded fromthe drying chamber other than that purposely admitted thereto andcompletely subject to control.

It is a further important object of the invention to provide adehydrating process applicable to a wide variety of comminutedmaterials, in-

eluding not only forage crops, but also seaweed, malt, or materialsrequiring either surface drying or dehydration. Where the process isused for drying agricultural produce it is a further purpose of theinvention to leave such produce with substantially its original color,flavor, taste and food value to a degree not heretofore achieved in anydehydration process involving other than laboratorymethods.

By way of exemplifying an apparatus suitable for the process hereindisclosed, I have shown in the accompanying drawings the dehydratingapparatus claimed in the application aforesaid.

In the drawings:

Figure 1 is a side elevation of apparatus embodying this invention, thewall of the drum and a portion of the heating unit being broken away toexpose the interior construction in vertical axial section.

Figure 2 is a plan view of the apparatus shown in Figure 1.

Figure 3 is a section takenin the plane-indi-- cated at 3-3 in Figure 1.

Figure 4 is a section taken on the line 4-4 in Figure 1.

Figure 5 is a diagram of the system of controls. Figure 6 is an enlargedfragmentary detail be drawn by a tractor to pull the apparatus fromplace to place. The dehydrating mechanism will be described in the orderof travel of material through the machine, after which I shall describethe actuating connections and controls.

Feeding device The material to be dehydrated is preferably comminutedwith such uniformity as is possible in order that the pieces of materialmay be approximately of the same size and may have their cut endsexposed for the delivery of their water content to the drying gases. If,however, the material to be dried is grain or malt, it is generallyhandled without comminution.

The material is deposited in the hopper 15, the bottom of whichcomprises a conveyor 16 operating in the conveyor trough made up ofsections 1'7, 18, and 19. The various sections are hinged together andmay be drawn upwardly by means of cable 20 to the collapsed positionindicated by dotted lines in Fig. 1. The fact that the hinge betweensections 18 and 19 is located at the upper surface of such sections, andthe hinge between sections 17 and 18 is located at the lower surface ofthese sections, results in equalizing the tenslon and slack produced inthe conveyor stretches by hinged collapse of the trough.

The forward wall of the hopper comprises a gate which is shown in dottedlines at 21 in Fig. 1, and may be adjusted vertically by means of thescrew 22 operated by hand wheel 23. Clearance between this gate and theconveyor 16 will determine the depth of material which will pass fromthe hopper upon the conveyor apron. This depth will be controlled bymanually varying the position of gate 21 in accordance with the kind ofmaterial to be dried. It will be obvious that this apparatus constitutesa means for regulating the rate of feeding the dehydrating apparatus. Ifthe material is wet, it will be desirable to reduce the thickness of thelayer thereof on the conveyor in order not to feed the machine toorapidly. If, on the other hand, the material is relatively dry, the gate21 can be raised to allow a relatively thick layer of material to passupwardly on the conveyor.

At its upper end the conveyor 16 discharges into a throat 25 throughwhich delivery of the green material is controlled by means of a rotaryvalve 26. This valve cuts off direct communication with the outer airand thereby prevents air from entering in any substantial quantitieswith the material to be dried. The rate of rotation of the valve will beso determined that the valve will carry away the material atsubstantially the exact rate at which it is delivered into the throat 25by the conveyor.

Source of hot gases The material discharged by the valve 26 falls into astream of heated gases traversing the feeding nozzle 27 which leads fromthe mixing chamber 28 into the central compartment of the drum 30, laterto be described. The movement of gases through nozzle 2'1 is producedsolely by the partial vacuum or depression existing within the drum, dueto the action of a powerful exhaust fan at its outlet end. The gasesutilized include such air as is admitted through the port 31 under thecontrol of door 32, together with the products of combustion incident tothe burning of fuel in one or more combustion chambers, of which two areillustrated at 33.

While coal or any other fuel may be utilized for the purpose of thisinvention, I prefer for several reasons to use oil or gas. Thehydrocarbon furnaces illustrated in the drawings are not only eflicient,but minimize the size of the heating plant, andtheir output is virtuallyfree of sumcient quantities of soot and odorous vapors to affect theappearance or taste of the material to be dehydrated.

The two combustion chambers 33 are substantially cylindrical, and therespective fuel nozzles 34 are arranged tangentially as shown in Fig. 1.The products of combustion will travel helically through the respectivecombustion chambers toward the mixing chamber 28, which they reachthrough the openings 35 in the partition walls 36.

In the mixing chamber 28 the products of combustion are mixed with theair, if any, admitted through door 32.

The diameter of the feeding nozzle 27 will be so determined withreference to the capacity of the machine, that the velocity of gasestherein will at all times be sumcient to project the wet materialsupplied through throat 25 pneumatically into the interior of drum 30.The drum is so arranged, however, that the velocity of gases passingthrerethrough is reduced repeatedly. The structural organization of thedrum is so important to the successful dehydration of material passingtherethrough, that it will be described in some detail.

The dehydrating drum The drum 30 is a boiler-like structure mounted toturn as a unit upon the wheels 38 which turn with shafts 39 extendinglongitudinally of frame 10, and drive the drum. In order to secure thecompact form so necessary for a portable dehydrating outfit of largecapacity, and in order also, to secure that repeated reduction in gasvelocity which contributes so much to the successful dehydration ofmaterial passing through the drum, the drum is preferably made up tocomprise a plurality of concentric tubes 40, 41 and 42. The

drum through which the material enters by means of nozzle 2'1. Itterminates in spaced relation to a disk-like bailie 43 which is spacedfrom the opposite end of the drum and closes the end of the intermediatetube 41. The intermediate tube in turn is spaced from the front end ofthe drum as shown at the left in Fig. 1. A series of radial struts 44braces the several tubes from each other to make a rigid assembly.

The rigidity of the individual tubes is enhanced by longitudinallyextending flanges which may be forwardly inclined in the direction ofdrum rotation, as shown at 45, or may be radial as shown at 46. Theseflanges act as pockets to lift the green material to the top of therespective drum, and to drop it into the path of the gas streamtraversing the drum. It will be understood that the gas entering throughnozzle 27 passes the whole length of the innermost tube 40, is turned bybaflie 43, and passes toward the front of the machine the whole lengthof the intermediate tube 41; and is turned by the front end of the drumand passes to the back end of the machine the whole length of the outertube 42. It then passes centrally around the face of balile 43 andthrough the outlet duct 47. The constantly increasing cross section ofthe various compartments of the drum causes a corresponding diminutionof velocity of the gases, except at the points where the gases arechanging their direction. At these points the area is purposelyrestricted to increase momentarily the gas velocities, and thereby toprevent the lodging of material at these points.

Means for handling dried materials It will be obvious that the weight ofthe material to be dried will be reduced proportionately to the amountof water extracted in the drying operation. The amount of water inmaterials ordinarily dried is generally from 50% to of the total weightof the material. Consequently each particle of material undergoes a verygreat change in weight as it progresses through the machine. This factis utilized to control automatically the time for which the variousparticles remain in the machine.

When the blast of hot gases entering through nozzle 27 pneumaticallyprojects the green material into the inner tube 40 of the drying drum30, the weight of the various particles of material to be dried causesthem to drop to the bottom of the tube. In the rotation of the tubethese particles are carried by flanges 45 to the top of the tube wherethey fall from the flanges through the blast of hot gases. Naturally,the lighter particles will be advanced along the drum by the blast ofgases more rapidly than will be heavier particles. This is veryadvantageousbecause the gases at this point are at maximum temperature(averaging about 1000 or 1500 degrees Fahrenheit, athough a great rangeoftemperature is practicable above and below the points specified) andprolonged exposure of minor particles of forage to such high temperaturewould be deleterious, and would result in too great a drying action,notwithstanding the fact that no material oxidation could occur becauseof the almost complete absence of oxygen.

The amount of air admitted through door 32 is not sufllcient to supportcombustion, and the air admitted through the burner ports 34 delivers upsubstantially all of its oxygen for the combustion of the hydro-carbonfuel. Even though combustionof the material to be dried is impossible,therefore, it is an advantage to have the very small and light particlesof such material move through the machine more rapidly than the heavierparticles, and this occurs automatically as the particles aresuccessively dropped across the path of the blast of gases.

The rate of evaporation from all of the particles will be very high dueto the tremendous volume of very dry gases to which the particles areexposed, and due also in large part to the fact that the pressuresexisting in the drying drum are sub-atmospheric.. The material in itswettest form is exposed to the gases when they are hottest and driest.The relatively large quantity of moisture, and also the high velocityand rapid reduction of temperature, keep the material from burning andflavor change in the presence of heat which would be excessive upondrier material or for longer periods.

It will be noted that no blower is employed at the inlet end of thedevice, except that which supplies the air blast required for theparticular oil burners illustrated. The current of gas through thepassages of the drying drum or chamber is created almost solely by theaction of the exhaust fan at the outlet.

As the particles of average size and larger deliver up their moisture,they too become light and move more and more rapidly through tube 40,until ultimately a continuous stream of material is being delivered fromtube 40 into the larger concentric tube 41.

The diameter of tube 41 is so much greater than that of tube 40 that thevelocity of the current of drying gases therethrough is materiallyreduced. Another factor contributing to the reduction of gas velocity inthe successive tubes of the drum, is the decrease in temperatureoccasioned by the evaporation of moisture. It will be noted that thereis very little'heat loss by radiation in this device, due to the factthat the outer compartment therein is in a position to intercept anyheat radiating from the two inner compartments. By the time the gasesreach the outer compartment, their temperature is very much reduced sothat the high radiation loss which would occur if the outer shell werefilled with gas at the original high temperature, is

. quite largely avoided.

In the intermediate shell and the outer shell, as well as in the innershell or tube 40, the rotation of the drum is continually carryingmaterial to the top thereof and releasing it to fall through the gascurrents to the bottom. In practice, the material is not discharged allat once but commences to drop about 120 before reaching the extreme topand continues tobe discharged until as soon as it is fully dried, andthe result tends strongly to equalize the extent to which all particlesof material issuing from the machine are dried.

From the outer compartment within the exterior shell 42 of the dryingdrum, the dried material and stream of gases passes centrally about thebaffle 43 and through the outlet passage 47 which is laterally extendedat 49 to the axial inlet of the fan casing 50. This fan must besufliciently large and powerful to produce the desired current of gasthrough the drum 30. Its tangential delivery spout 51 discharges into apipe 52 which leads across the front of the machine to the top of anordinary centrifugal separator 53 into which the gas and material isdelivered tangentially to effect the separation thereof by the vortexthus created within the separator. The water laden gas then issues fromthe opening 54 at the top of the separator. It will be found that thegas will be virtually saturated at its discharge temperature if thevarious factors relating to eflicient drying have been properly workedout in accordance with the considerations hereinafter explained.-

. The dried material drops through the bottom opening 55 in theseparator into the receptacle 56 at the inlet of a pneumatic conveyorfan 57. This fan may comprise an ordinary centrifugal blower of whichthe discharge pipe 58 may lead to a silo, bin, bagging machine, or anyother objective.

While all the particles of material issuing from the machine will bemore or less uniformly dried to approximately the same degree for thereasons above explained, this degree of dryness may vary in accordancewith a large number of factors including particularly the temperature,dryness, and rate of flow of the gases passing through the drying drum,the rate at which wet material is supplied through the machine, and thedegree of wetness thereof, and also the temperature and the extent towhich the natural juices of the material are exposed for evaporation.

Those skilled in the art will perceive that for any given gas conditionand kind of material. the amount of water which will be extracted by thedehydrating apparatus will be a relatively fixed quantity, andconsequently the dryness of the discharged material may depend directlyupon the rate at which the material is fed to the machine. Particularlyif the rate of feeding exceeds the capacity of the machine forextracting moisture to the desired degree of dryness, the product maynot be sufllciently dehydrated. The effect of the incoming material isalmost immediately manifested in reduction of the temperature of thegases supplied from the mixing chamber 28, both by direct absorption ofheat by the material itself, and by the evaporation which occurs inproportion to the presence of quantities of wet material.

In view of the foregoing considerations, it is very important in amachine of this character to feed the machine in such a way that therate at which wet material is supplied thereto, can be maintained almostperfectly uniform for any given condition. It is also desirable to beable to vary the rate of feeding instantaneously to correct any factorstending to upset the balance which has been found to give the desireddehydration. The feeding conveyor and leveling gate 21 have been foundvery satisfactory for maintaining a uniform rate of feeding. Thecontrols and driving connections now to be described may be set to careautomatically for any matters requiring correction to produce auniformly satisfactory product.

Driving connections It is contemplated that the dehydrating apparatuswill be driven from the tractor which pulls it from place to place. Inthe dehydrating apparatus the source of power is the pulley 60 on blowershaft 61. From this as a belt 62 drives 1 the blower 63 which suppliesan air blast through pipes 64 to the two burners, the blast of eachburner being individually controlled by the gate 65 appearing near theburner in Fig. 1. It would not be impractical to control the burnersautomatically by the same means hereinafter described, but ordinarilythis is unnecessary for reasons hereinafter mentioned.

Shaft 61 also drives, by means of a belt or chain 70, the runner of theblower fan 57 and, on the same shaft, the oil pump '71 which comprises agear pump illustrated diagrammatically in Fig. 2, and shown moreparticularly in Fig. 5.

From the primary driving shaft 61 a chain '72 drives a jack shaft 73from which another chain 74 drives one of the longitudinally extendingshafts 39 "for the support and drive of the drum. Chain 75 connects thetwo drum driving shafts so that the respective rolls 38 turnsimultaneously in the same direction to rotate the drum.

Power for the operation of the rotary valve 26 .and the conveyor 16, istaken from one of the shafts 39 as shown in Fig. 2. A chain '17 leadsfrom shaft 39 to the driving shaft of a commercial rate changing device'78, of which the power output shaft is connected by chain 79 with the,conveyor drive shaft 80. The shaft 80 in turn is connected by chain 81with the rotary valve. This arrangement insures that the rotary valvewill operate as rapidly as material is supplied thereto, and it providesfor simultaneous variation in the rate of operation of the conveyor andvalve in accordance with the adjustment of the rate changing mechanismdesignated in its entirety by reference numeral 78.

The system of controls Oil contained in the supply tanks 85 is utilizedfor controlling the operation-of the dehydrator, as well as forsupplying the burners 34. The use of two separate tanks is merely forconvenience in positioning the feed conveyor trough, and the two tanksmay function as one, being interconnected. The oil supply line 86 runsthrough a filter 87 and the intake side of pump '11 from whichthe oil isdischarged at relatively high pressure. If the fuel oil is used forregulation the pressure used amounts to fifty pounds. This pressure ismaintained by a loading valve 88 in a by-pass line 89 around the pump,so that any excess of pressure will leak through the by-pass to maintainthe pump output uniform.

From the output of the pump a high pressure line 90 leads to the burners34 where air, supplied through pipe 64, is carbureted and discharged forcombustion into the chambers 33. The helical path of flame and gases inthe combustion chamber insures a suflicient length of travel so thatthorough combustion may result before the products of combustion passthrough the foraminous walls 36 into the mixing chamber 28.

From the pump another high pressure line 91 leads to the reducing valve92, where the pressure is reduced sufllciently so that it can be handledby the thermostatically controlled valve 93.

I have found, and it is important to note here, that in normal operationof the device herein disclosed, the dryness of the finished product willbe substantially directly proportioned to the temperature of the gasesat the outlet end of the machine. If this temperature rises too high, itwill invariably be found that the finished product has been toocompletely dried. If this temp'erature drops below a proper value, itwill be found that the material is not sufllciently dry.

Accordingly, I employ at 93 a commercial thermostatic valve mounted onthe exhaust passage 49 to respond to gas temperatures therein. There isan adjustment at 94 whereby the'valve may be set to operate at anydesired exhaust gas temperature. This is important, because differentproducts require dehydration to different degrees, and the adjustment at94 enables the operator to secure exactly the desired dehydration. Inpractice fifteen pounds pressure is delivered from the reducing valve'92to the thermostatically controlled valve 93. In the operation of theparticular thermostatic valve shown at 93, there is a certain amount ofwaste oil which is by-passed through pipe 95 to the pump inlet. Theoperation of the thermostatic valve is such that pressure establishedbeyond the valve when the valve is open, is relieved through the pipe 95upon the closing of the valve.

When the thermostatically controlled valve 93 is open, oil pressure iscommunicated through the low pressure line 96 to the damper control 9'!by means of which the door or damper 32 for admitting fresh air into themixing chamber 28, is operated. A tension spring 98 normally holds thedamper closed, but is overcome by oil pressure when the thermostaticvalve opens.

A branch pipe 99 from the low pressure line 96 leads to the pressureoperated controller 100 of valve 101. This valve is located in the highpressure branch 102 of line 90, and leads to a pressure operatedcontrolling device 103 for the rate changing mechanism '78. In order torelieve the controlling device 103 of pressure established therein whenvalve 101 is opened, I provide a by-pass valve at 104 which isconstantly open, and through which a small quantity of oil leaks at alltimes from pipe 105 to the supply -main 86.

The control apparatus is preferably not of the type which isalternatively in its extreme positions. On the contrary, the apparatusdisclosed will maintain-at all times a graduated rate of feedingmaterial and air, which is directly in accordance with the requirementto produce a uniform temperature and hence a uniform product at thedelivery end of the drum.

It will be noted that the burners may, if desired, be set manually foroperation at maximum efliciency and continue at all times in suchoperation without automatic control, although obvi- "ously this maybe'used when desired. In the presinflux of cold air, while relativelysmall in volume as compared with the hot gases delivered to the mixingchamber 28 by the burners and associated mechanism, will immediatelytemper such gases, and inasmuch as it takes only a few seconds for gasto pass through the apparatus from inlet to inlet, the result of thetempering will immediately become effective, on the thermostat and tendto prevent over-control.

It is very important to note, also, that the infiux of air throughdamper 32 accelerates the gas current through the drum so that I notonly temper the heat but increase the speed at which the material moves,thereby decreasing the period of about three minutes for which materialof average weight remains in the drum.

In order to exclude extraneous air and thus enable the accuratefunctioning of-the controls above mentioned, I not only pass the greenmaterial through the rotary feeding valve 26, but I also provide aninexpensive but relatively airtight joint between the rotating drum andthe feeding nozzle 27 at one end, and the discharge pipe 4'7 at theother. The feeding nozzle and discharge pipe have annular flanges asshown at 110 in the detail view in Fig. 6. Obviously, these flanges arenon-rotatable. Their exterior faces are preferably disposed insubstantially the exact plane of the respective heads of the drum.

Secured to each drum head is an annular gasket 111 which may be made ofasbestos paper, preferably of the heavy sort used in brake and clutchlining. The depression existing within the drum causes air pressure onthe annular gasket 111 to hold the gasket tightly in contact with theannular flange 110 with respect to which it rotates. As a result, air isvirtually completely excluded from passing through this joint, and theamount of friction involved is negligible. The life of the gasket islong, and replacement thereof is easy.

The process Although the process here involved has been described inconnection with details of the mechanism shown in the accompanyingdrawings, I shall review it briefly before stating my claims.

The material to be dehydrated is prepared, if necessary, to reduce it asnearly as possible to pieces or unit particles of uniform size.Preferably this will be done by comminution or cutting in order that theraw ends of the particles of material may be exposed for the evaporationof the liquid content thereof.

The material is fed to the machine at a rate proportioned to thedehydrating capacity of the machine and the amount of dehydrationrequired. In delivering the material to the machine it is placeddirectly into the path of very highly heated gases in an almost totalabsence of oxygen. The high temperature of the gases renders them highlyefllcacious for the absorption of moisture, and the fact'that they aresubstantially oxygen-free enables much higher temperatures to be usedthan would otherwise be possible without changing the nature of theproduct.

The material is at first heavy with moisture, and in its repeatedtraverse across the stream of hot gases during the rotation of the drumor other means employed for this purpose, the material will be advancedbut slightly by the gases in their direction of travel. As the operationcontinues, however, the moisture content in the material is delivered upto the heated gases and the material gradually becomes lighter while thegases are rapidly cooled, both by contact with the material and byevaporation of moisture therefrom.

As the material dries and loses weight it is moved more rapidly by thegas stream in the course of successive traverses of the gas stream. Thegas stream, however, is increasing in cross section and undergoing aconsequent decrease in velocityso that from time to time the progress ofthe material is retarded until it is sufficiently dry and light so thateven the heaviest particles can be moved from the machine by therelatively slowly moving gas stream at the discharge end.

Throughout the movement of the material the gas stream is subject to adepression further accelsrating the evaporation of moisture from thematerial. The combined effect of the various factors herein disclosed issuch that dehydration is carried on with less consumption of fuel thanthat estimated by skilled agricultural engineers to be required at 100%efliciency.

Uniformity of result is established in part through the use of the gasstream to advance the material in proportion to its dryness as thematerial is delivered transversely of said stream. Uniformity isadditionally dependent upon regulation of gas temperature and the rateof feeding material in accordance with the temperature of the gas at thedischarge end of the machine.

I claim:

l. The method of dehydration which consists in establishing a current ofhighly heated drying gas substantially free from oxygen, feedingtherethrough and advancingsolely by the current the material to bedried, and automatically regulating the temperature of gas supplied tosuch material in accordanace with the temperature of the spentrelatively cool gas which has acted thereon.

2. The method of dehydration which consists in establishing a current ofhighly heated gas substantially free from oxygen, deliveringcontinuously thereto and subsequently transporting solely by the currenta stream of material to be dried thereby, and regulating both thetemperature of said gas and the rate of feeding such material inaccordance with the temperature of the spentrelatively cool gas whichhas acted upon such material. I

3. The method of dehydration which consists in establishing a current ofhighly heated gas substantially free from oxygen, deliveringcontinuously thereto and advancing solely by the current a stream ofmaterial to be dried thereby, and regulating both the temperature ofsaid gas and the rate of feeding such material in accordance with thetemperature of the spent relatively cool gas which has acted upon suchmaterial, the rate of feeding being increased and the temperature of thegas to which such material is exposed being decreased upon theoccurrence of an increase of temperature in the spent gas which haspreviously acted upon material supplied thereto.

4. The method of dehydration which consists in establishing a current ofheated gas substantially none of which gas has been previously used fordehydration, delivering to the gas of saidcurrent a stream of materialto be dehydrated, moving the stream of material in the same direction asthe current of gas, regulating the relation between the temperature ofsaid gas and the relative rates of movement of the gas and stream ofmaterial in accordance with the temperature of gas which has acted uponsuch material, and permanently discharging the gas from contact with thematerial, the regulation being so conducted as to increase the rate ofevaporation when said temperature rises and to decrease said rate whensaid temperature falls, whereby to produce a substantially uniformoutput. I

5. The method of dehydration which consists in the establishment of adehydrating current by continuously withdrawing and permanentlydischarging from the drying chamber substantially all of the gasadmitted thereto, and supplying highly heated relatively dry gas to saidchamber at such a rate as to maintain a partial vacuum therein,delivering to the dehydrating current of gas through said chamber asubstantially continuous flow of material to be dried thereby andpropelled by said current through said chamber, gradually increasing thecross section of the current through said chamber toward the dischargeend thereof, whereby the rate of advance of said material by saidcurrent will be a function of the dryness of said material, admittingair to the heated gas whereby not only to decrease its temperature butto increase its velocity in said current, and regulating the admissionof such air in accordance with temperature of the gas withdrawn anddischarged from said chamber, whereby to control the rate of drying ofsuch material not only by the temperature of said gas but also by therate of pneumatic propulsion of the material by said gas in saidcurrent.

6. The method of dehydration which consists in delivering uniformlysized material to be dried into a current of highly heated gassubstantially free from oxygen and having a gradually diminishingvelocity sufliciently high to advance all of the admitted material inthe direction of travel of the gas at a rate of speed dependent upon theweight of the particles, repeatedly precipitating the material throughthe current during said advancement while subjecting the deliveryend ofthe current'to sub-atmospheric pressure, and regulating the initialtemperature of the gas and the rate of said delivery by the temperatureof the spent gas at the discharge end of the current to maintain auniform condition of the finally treated material. I

'7. The method of dehydration which consists in establishing a currentof heated gas substantially none of which gas has been previously usedfor dehydration, maintaining the gas in said current undersub-atmospheric pressure, delivering to the gas of said current a streamof material to be dehydrated, repeatedly dropping such materialtransversely of the stream of gas while gradually increasing the crosssection of the stream, whereby to reduce its velocity, regulating therelation between the temperature of the gas and the relative rates ofmovement of the gas and stream of material in accordance with thetemperature of gas which has acted upon such material, and permanentlydischarging the gas from contact with the material, the regulation beingso conducted as to increase the rate of evaporation when the temperaturerises and to decrease said rate when the temperature falls, whereby toproduce a substantially uniform output.

8. The method of dehydration which consists in establishing a current ofheated gas, substantially none of which gas has been previously used fordehydration, delivering to the gas of said current a stream of materialto be dehydrated, moving the stream of material in the same direction asthe current of gas, permanentlydischarging the gas from contact with thematerial, and regulating the rate of movement of the stream of materialin' accordance with the temperature of gas which has acted upon saidmaterial, the regulation being so conducted as to increase the rate ofevaporation when the temperature rises, and to decrease said rate whensaid temperature falls, whereby to produce a substantially uniformoutput.

GERALD D. ARNOLD.

